The invention relates to the optimal use of two heat sources with differing amounts of heat and heat temperatures, for example waste heat from the engine and exhaust system of internal combustion engines, by means of ORC turbomachinery and piston engines. The invention is characterised in that the vaporous ORC working fluid with a saturated vapour line in the P-h diagram that inclines sharply to the right is expanded in at least two steps and said ORC working fluid is cooled between said two or more steps in such a way that the heat obtained in the cooling process is fed to the liquid ORC working fluid in a pre-heating device II in a temperature range lying above that of the waste heat from the engine.